This invention relates to a device for controllably supplying hydraulic pressure and particularly to a master cylinder particularly useful for activating a hydraulically controlled clutch of a motor vehicle.
Motor vehicles employing manually shiftable transmissions typically include a manually actuated drive clutch. The clutch is employed to selectively couple and uncouple the motor vehicle engine output with the drive transmission thereby permitting gear changes. Several types of clutch actuation systems are currently employed. Mechanically actuated types employ linkages or cables to effect clutch engagement and disengagement. Another type, with which this invention is particularly adapted, employs a remotely mounted slave cylinder which responds to a hydraulic pressure source to cause engagement or disengagement of the clutch as a fluid pressure responsive piston is caused to translate within the slave cylinder bore. For this latter type of clutch actuation system, a clutch master cylinder is provided which supplies the fluid pressure signal to the slave cylinder in response to forces applied to an internal slidable plunger exerted by foot pressure of the motor vehicle operator on a movable clutch pedal within the interior compartment of the vehichle. For either type of clutch actuation system, engagement and disengagement occurs due to reciprocal translation of a clutch release or throw-out bearing which engages rotating fingers of a clutch pressure plate. These fingers cause the clutch plate to selectively clamp or unclamp a clutch disc between itself and the engine flywheel, thereby effectuating the coupling and uncoupling function. Clutch discs are typically covered with friction material which wears through cycles of clutch actuation, therefore, means for compensating for such wear and its effect on the actuation system is needed.
Hydraulically actuated clutch master cylinders heretofore available employ a slidable plunger within a cylinder bore where the plunger is biased by spring force in a clutch engaged position. Due to fluid displacement within the hydraulic circuit, which occurs as the friction material of the clutch plate is worn away, a reservoir for hydraulic fluid must be provided for the master cylinder. Heretofore, fluid actuated clutch cylinders employed a separate or integrally mounted container of hydraulic fluid mounted above the master cylinder such that as fluid displacement occurs, the reservoir could provide or accept fluid. Such action by the reservoir occurs when the plunger uncovers a port communicating the master cylinder working chamber with the fluid reservoir. This configuration necessitated that the fluid reservoir be located above the master cylinder in order to prevent air ingestion within the hydraulic circuit and to provide gravity feed of fluid to the master cylinder. This requirement of mounting a fluid reservoir above the master cylinder requires an externally mounting reservoir or a machined clutch master cylinder housing providing an integral reservoir disposed above the housing. The necessity of providing such a reservoir, besides adding costs, tends to limit the types of production techniques which may be employed in fabricating the master cylinder housing.
In view of these above considerations, it is a principal aspect of this invention to provide a fluid activated clutch master cylinder of simplified construction and which may be produced at a reduced cost. It is another principal aspect of this invention to provide a clutch master cylinder housing which may be fabricated from relatively inexpensive techniques such as the deep forming of metal.
The above principal aspects of this invention are provided by incorporating a hydraulic fluid reservoir internally within the master cylinder housing. Specifically, the fluid reservoir chamber is a cylindrical chamber extending colinearly with the master cylinder working chamber and formed by a reduced diameter section of the same tube which forms the actuation plunger cylinder. A low spring constant coil spring is provided which biases a reservoir plunger within the reservoir to ensure that the hydraulic fluid therein is lightly compressed to avoid the introduction of atmospheric gases within the hydraulic circuit.
As a further further of the invention, the fluid contained within the reservoir may be pressurized to a greater than atmospheric pressure so that it will act to provide a degree of boost to the hydraulic system.